1. Field of the Invention
The present invention relates to an inverter control apparatus which is used for variable speed drive of a rotary machine, and a motor driving system using the same.
2. Description of the Related Art
FIG. 1 is a block diagram showing the circuit structure of a motor driving system using a conventional inverter control apparatus. A method of changing the frequency of 3-phase AC (alternating current) power Acc supplied to an induction motor is known as one method of controlling rotation speed of the induction motor. The conventional motor driving system is composed of a 3-phase AC power supply 50, an inverter control unit 20, a variable speed driving unit 60, and an induction motor 11 with a rotation frequency detecting unit 12 for a load. The variable speed driving unit 60 is composed of a rectifier 61 and an inverter 62. The variable speed driving unit 60 is used to control the rotation frequency of the induction motor.
The 3-phase AC power supply 50 supplies 3-phase AC power with a constant frequency (60 Hz) to the variable speed driving unit 60. The variable speed driving unit 60 is composed of a rectifying unit 61 and a current type inverter 62. The rectifying unit 61 rectifies the 3-phase AC power into DC power in response to a rectifier current instruction signal Id* from the inverter control unit 20. The current type inverter 62 inverts the DC power into 3-phase AC power Acc in response to an inverter frequency instruction signal fe* from the inverter control unit 20. Thus, the variable speed driving unit 60 controls the frequency of the 3-phase AC power Acc. The 3-phase AC power Acc is supplied to the multi-polar induction motor 11.
The inverter control unit 20 is composed of converters 21 and 22, adders 23 and 26, a speed control section 24, a slide calculating section 25, and a current calculating section 27.
For slide frequency control, a rotation frequency of the multi-polar induction motor 11 (the number of poles is p) is detected by the rotation frequency detecting unit 12 such as an encoder and a signal form indicative of the detected rotation frequency is supplied to the converter 22 of the inverter control unit 20. The converter 22 converts the detected rotation frequency signal form into a 2-pole conversion detected rotation frequency signal fr2 which is supplied to the adders 23 and 26. A multi-polar rotation frequency instruction signal form* is supplied to the converter 21 from the outside, and the converter 21 converts the multi-polar rotation frequency instruction signal form* into a 2-pole conversion rotation frequency instruction signal fr2*, which is supplied to the adder 23.
The adder 23 subtracts the 2-pole conversion detected rotation frequency signal fr2 from the 2-pole conversion rotation frequency instruction signal fr2*, and supplies the subtracting result to the speed control unit 22. The speed control unit 22 generates a 2-pole conversion torque instruction signal T2* from the subtracting result, and supplies to the current calculating section 27 and the slide calculating section 25. The current calculating section 27 calculates the rectifier current instruction signal Id* from the 2-pole conversion torque instruction signal T2* and supplies to the rectifying unit 61 of the variable speed driving unit 60.
The slide calculating section 25 calculates a slide frequency instruction signal Fs* from the 2-pole conversion torque instruction signal T2*. The adder 26 adds the slide frequency instruction signal Fs* and the 2-pole conversion detected rotation frequency signal fr2 to produce the inverter frequency instruction signal fe*, which is supplied to the current type inverter 62 of the variable speed driving unit 60.
In conjunction with the above description, an inverter control apparatus is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 11-69880). In this reference, an inverter inputs DC power from a DC power supply through a filter capacitor which is provided on the input side of the inverter, and supplies AC power with a variable voltage and a variable frequency to an AC motor to drive the AC motor. A voltage increase suppressing torque instruction correcting section of the inverter control apparatus inputs a capacitor DC voltage applied to the filter capacitor and an operation torque instruction, and outputs a first torque instruction to reduce regenerative torque for suppressing the increase of the DC voltage when the DC voltage increases. A change rate limiting section of the inverter control apparatus limits the change rate of the first torque instruction to output a second torque instruction.
An object of the present invention is to provide an inverter control apparatus in which the stationary characteristics (such as effective values of voltage and current) of an inverter can be improved, and a motor driving system using the inverter control apparatus.
In an aspect of the present invention, a motor driving system for driving an induction motor with a rotation frequency detector, wherein the induction motor drives a load, and the rotation frequency detector detects a rotation frequency of the induction motor, includes a variable speed driving unit, and an inverter control unit. The variable speed driving unit is connected to the induction motor and has a capacitance at output. The variable speed driving unit rectifies first 3-phase AC power to produce DC power, and converts the DC power into second 3-phase AC power with a frequency, and drives the induction motor with the second 3-phase AC power. The inverter control unit generates a frequency instruction and a temporary current instruction based on the detected rotation frequency and a rotation frequency instruction at least. Then, the inverter control unit corrects the temporary current instruction based on at least one of first correction depending on the capacitance and second correction depending on a predetermined frequency component of the temporary current instruction to produce a current instruction, and controls the variable speed driving unit based on the frequency instruction and the current instruction.
The variable speed driving unit may include a rectifying unit and a current type inverter. The rectifying unit rectifies the first 3-phase AC power in response to the current instruction to produce the DC power. The current type inverter has the capacitance at the output, and inverter converts the DC power into the second 3-phase AC power with the frequency in response to the frequency instruction.
Also, the inverter control unit may include a first correcting section which corrects the temporary current instruction for current flowing into the capacitance in the first correction to produce the current instruction. In this case, the first correcting section may correct the temporary current instruction based on a first correction factor to produce the current instruction. The first correction factor is determined based on the capacitor, a self-inductance of a stator of the induction motor stator, a mutual inductance between the stator and a rotor in the induction motor, a self-inductance of the rotor of the induction motor, a resistance of the stator of the induction motor, a resistance of the rotor of the induction motor rotor, and slide.
Also, the inverter control unit may include a second correcting section which corrects the temporary current instruction based on a second correction factor in the second correction to produce the current instruction, wherein the second correction factor is determined such that the predetermined frequency component is set to a predetermined value.
Also, the inverter control unit may include a first correcting section and a second correcting section. The first correcting section corrects the temporary current instruction for current flowing into the capacitance in the first correction to produce a next temporary current instruction. The second correcting section which corrects the next temporary current instruction based on a second correction factor in the second correction to produce the current instruction, wherein the second correction factor is determined such that the predetermined frequency component is set to a predetermined value. In this case, the first correcting section may correct the temporary current instruction based on a first correction factor to produce the next temporary current instruction. The first correction factor is determined based on the capacitor, a self-inductance of a stator of the induction motor stator, a mutual inductance between the stator and a rotor in the induction motor, a self-inductance of the rotor of the induction motor, a resistance of the stator of the induction motor, a resistance of the rotor of the induction motor rotor, and slide.
In another aspect of the present invention, an inverter control apparatus is for controlling a variable speed driving unit which rectifies first 3-phase AC power to produce DC power, and converts the DC power into second 3-phase AC power with a frequency to drive an induction motor. The inverter control apparatus include a frequency instructing section and a current instructing section. The frequency instructing section generates a torque instruction based on a rotation frequency of the induction motor and a rotation frequency instruction at least and controls the frequency of the second 3-phase AC power based on the torque instruction and the rotation frequency of the induction motor. The current instructing section generates a temporary current instruction from the torque instruction, corrects the temporary current instruction based on a capacitance and an impedance of the induction motor, and controls the variable speed driving unit based on the corrected current instruction, the variable speed driving unit having the capacitance at output connected to the induction motor. In this case, the current instructing section may further correct the corrected current instruction such that a predetermined frequency component of the corrected current instruction is set to a predetermined value.
In still another aspect of the present invention, an inverter control apparatus outputs a control signal to a variable speed driving apparatus which drives an induction motor in a variable speed in response to the control signal. The inverter control apparatus includes a control signal generating section which generates the control signal based on a capacitance at an output terminal set of the variable speed driving apparatus which is connected to the induction motor at the output terminal set.
The control signal is determined based on parameters associated with a rotor and a stator of the induction motor.
Also, the control signal satisfies the following equation:
Idc*=Kcxc2x7Id* 
where
Idc*: the control signal,
Id*: an auxiliary control signal to be outputted as the control signal when the capacitance is not considered,
Kc: a coefficient Kc determined based on a self-inductance of a stator of the induction motor, a mutual inductance between the stator and a rotor of the induction motor, a self-inductance of the rotor of the induction motor, a resistance of the stator of the induction motor, a resistance of the rotor of the induction motor, and a slide quantity.
Also, the control signal generating section may generate the control signal to compensate for a capacitor current flowing into the capacitance.
Also, the control signal generating section generates the control signal based on a frequency instruction signal to instruct a frequency of an output of the variable speed driving apparatus, a self-inductance of a stator of the induction motor, a mutual inductance between the stator and a rotor in the induction motor, a self-inductance of the rotor of the induction motor, a resistance of the stator of the induction motor, a resistance of the rotor of the induction motor, a slide quantity of the induction motor, in addition to the capacitance.
In yet still another aspect of the present invention, an inverter control apparatus outputs a control signal to a variable speed driving apparatus which drives an induction motor in a variable speed in response to the control signal. The inverter control apparatus includes a control signal generating section which generates the control signal based on a frequency component contained in an input signal and a remaining frequency components of the input signal. In this case, the control signal generating section multiplies the input signal and a reciprocal of a ratio of the frequency component to the input signal and generates the control signal based on the multiplication result.
In further another aspect of the present invention, an inverter control apparatus outputs a control signal to a variable speed driving apparatus which drives an induction motor in a variable speed in response to the control signal. The inverter control apparatus includes a capacitor correction signal generating section and a control signal generating section. The capacitor correction signal generating section generates a capacitor correction signal based on a capacitance connected with an output terminal set of the variable speed driving apparatus. The control signal generating section generates the control signal based on an inverter frequency component contained in the capacitor correction signal and a remaining frequency component of the capacitor correction signal other than the inverter frequency component.
In a still further another aspect of the present invention, a motor driving system includes a variable speed driving apparatus which supplies an AC control power generated based on a control signal to an AC motor to drive the AC motor in variable speed, and an inverter control apparatus which outputs the control signal to the variable speed driving apparatus. The variable speed driving apparatus includes a rectification section which rectifies AC power to generate DC power; and an inverter section which generates the AC control power from the generated DC power. The inverter control apparatus generates the control signal based on a capacitance connected with an output terminal set of the variable speed driving apparatus, an inverter frequency component of an input signal and a remaining frequency component of the input signal other than the inverter frequency component, and outputs the control signal to the rectification section.